Conventionally, an air conditioner for a vehicle, which has a slide door for air mixing, is described in Patent Document 1 (JP 2000-043535 A). In the vehicle air conditioner, a warm air passage is provided so that air passes through a heater core via the warm air passage in an air conditioning unit. Moreover, cold air passages, which bypass the heater core, are provided at upper side and lower side of the warm air passage.
The vehicle air conditioner includes a first slide door and a second slide door. The first slide door opens or closes an upper part of the warm air passage and the cold air passage located at an upper side of the warm air passage. The second slide door opens or closes a lower part of the warm air passage and the cold air passage located at a lower side of the warm air passage.
These slide doors moves approximately in an up-down direction. Thus, these slide doors are highly affected by their own weights, and a necessary operation force to move these doors upward may be thereby increased.
When the slide door is arranged to slide in a direction near to a horizontal direction in order to reduce the necessary operation force, dust or the like contained in air is likely to be accumulated in a groove which guides the sliding motion of the slide door.